Patent U.S. Pat. No. 4,588,923 describes a lamp adapted to various needs, such as person heating. A lamp adapted to radiant heating emits substantially only infrared radiation. When infrared radiation impinges onto the skin of a person, the radiation interacts with the nerve ends and creates a sensation of warmth for the person. The lamp described in this patent comprises a radiant source, such as a tungsten filament, which is housed in a lamp vessel comprising a gas such as argon, with a small quantity of a halide substance. The radiant source emits radiations both in the visible and infrared parts of the radiation spectrum. In order to transmit a large part of the infrared radiation and stop a large part of the visible radiation, the lamp vessel comprises a reflective film on its outer surface, which reflective film is adapted to transmit substantially only infrared radiation.
In such a lamp, the lamp vessel reaches a relatively high temperature, which depends on the linear power density of the lamp. The larger the linear power density, the larger the temperature of the lamp vessel. However, when the lamp vessel reaches a relatively high temperature, the reflective film, deposited on the lamp vessel, may be degraded, especially when the lamp has been used for a relatively long time. As a consequence, the linear power density of such a lamp is limited.